The invention relates to an improved process for the preparation of 2-halo-1-alkenes from light hydrocarbon streams.
Griesbaum, U.S. Pat. No. 3,377,389, Apr. 9, 1968, teaches that hydrogen chloride and hydrogen bromide will add to unsaturated compounds in accordance with Markovinkov's Rule and that allene (propadiene) and methylacetylene (propyne) are hydrohalogenated to give 2-halopropene.
Kovachic and L. C. Leitch, "Organic Deuterium Compounds", Can. J. Chem., 39, 363--374 (1961) teach that 2-halo-1-alkenes can be prepared by addition of hydrogen chloride to 1-alkynes. It is taught this addition can be performed in the presence of dibenzoyl peroxide or under ultraviolet illumination.
Arganbright, U.S. Pat. No. 3,142,710, teaches that propyne and propadiene can be selectively halogenated in the presence of propylene. Propylene containing minor amounts of propyne and propadiene together with hydrogen chloride are passed over a catalyst comprising mercuric halide deposited on a porous carrier, particularly one having high surface activity at a temperature in the range of from about 100.degree. C. to about 120.degree. C.
Schroeder and Slewka, French Pat. No. 1,505,099 (Dec. 18, 1965), teach that a C.sub.3 hydrocarbon stream may be purified by selectively removing propadiene (allene) and propyne (methyl acetylene) by reacting the C.sub.3 hydrocarbon stream with hydrogen chloride in the presence of hydrochlorination catalysts, in particular mercuric chloride on a support such as activated aluminum oxide, silica gel or activated carbon. The propadiene and propyne are selectively halogenated to prepare 2-chloropropene which is easily separated from the other components of the C.sub.3 light hydrocarbon stream.
Herbertz, "Von Aliphatischen Acetylenkohlenwasserstoffen ausgehende Synthesen", Chem. Ber., 92, 540-50 (1959), teaches two processes for the addition of hydrogen halides to alkynes. One is a mixed phase reaction wherein copper (I)-chloride is the catalyst. In the other, the alkyne is vaporized and mixed with hydrogen chloride and passed over activated charcoal in the presence of mercury at a temperature of 130.degree. C.
A process for selectively halogenating a 1,2-diene and a terminal acetylene with a hydrogen halide in the presence of other hydrocarbons wherein the yields of the 2-haloalkenes are substantially higher than prior art processes permit has been discovered.
The 2-halo-1-alkenes prepared by this process can be carbonylated and esterified to prepare acrylate esters if desired.
One such acrylate ester is methyl methacrylate which is prepared commercially from acetone which is treated with HCN to give 2-cyano-2-propanol which is then treated with 98 percent sulfuric acid to give a salt of propene-2-amide and sulfuric acid. The salt is then reacted with methanol to prepare methyl methacrylate and NH.sub.4 HSO.sub.4. This process requires a large purification scheme and the use of sulfuric acid and hydrogen cyanide.
It is desirable to prepare methacrylates without the use of sulfuric acid and hydrogen cyanide.